The present invention relates to wireless communication apparatus useful in a wireless communication system such as a code division multiple access mobile communication system, and to a method of transmitting power-control information in such a system.
Tight control of the transmitting power of mobile stations is an important requirement in code division multiple access (hereinafter, CDMA) communication systems. In conventional CDMA systems, the base station inserts power-control bits into the forward traffic channels, and the mobile stations raise or lower their transmitting power as directed by the power control bits. Typically, a mobile station adjusts its transmitting power many times per second in this way.
CDMA mobile communication systems employing packet communication have been undergoing research and development, however. In packet communication, at some times a base station may transmit packets continuously to a mobile station, but at other times packet transmission is intermittent. If power-control bits are inserted into intermittently transmitted packets, the receiving mobile station can execute power control only intermittently, which is unsatisfactory for system operation. Dummy packets can be transmitted to assure the regular arrival of power-control bits, but such dummy packets waste channel resources.
It is accordingly an object of the present invention to provide a wireless communication system in which power-control information can be transmitted regularly and often, even during intermittent transmission on traffic channels.
The invented method of transmitting power-control information from a first station to a second station in a wireless communication system establishes a power-control channel, distinct from the traffic channels in the wireless communication system, and transmits power-control information on the power-control channel. The first station may be either a base station or a mobile station. The power-control channel may operate only while another intermittent channel, such as a control channel, is inactive.
Power-control information may also be transmitted on the traffic channels. In this case, power-control information transmitted on the power-control channel is meaningful while the corresponding traffic channel is inactive, and is meaningless when the corresponding traffic channel is active.
If the wireless communication system is a CDMA system, the power-control channel has a different spreading code from the traffic channels.
The power-control information is preferably transmitted in superframes equivalent to two or more frames on the traffic channels.
The power-control channel may also be used to transmit additional information such as paging bits, acknowledgment bits, or flag bits indicating forthcoming transmission on the above-mentioned intermittent channel.
The invented wireless communication apparatus has a transmitting circuit (at the first station) or a receiving circuit (at the second station) for transmitting or receiving a power-control channel as described above.